Commonly used track chains for earthmoving vehicles comprise a plurality of track links. The track links are connected into two parallel endless chains by means of track link hinge joints having track pins joining the ends of adjacent pairs of links and spanning the space between the parallel chains. Drive sprockets drive the track chains and provide locomotion for the vehicle by acting against bushings upon the track pins.
For efficient and low cost operation, it is, of course, desirable to construct a track chain in a manner to provide for long, trouble-free operating life. All track parts are subject to wear because of the service they perform and the abrasive environment in which they operate. Recent developments in seals and lubrication methods promise to increase the life of some track parts measurably and it appears that the track bushing in its present form may well continue to be one of the first elements of the track to require repair or replacement.
Force for driving the tracks by sprocket is received upon a given portion of the bushing. Additionally, as each such bushing comes into engagement with or tends to be disengaged from the sprocket, the same portion of the bushing always contacts the sprocket. Since the bushing is conventionally pressed into the inner pair of links, it does not rotate while in engagement with the sprocket. There is, however, limited motion between the bushing and sprocket during engagement and disengagement of the sprocket with the bushing. The motion of the bushing against the sprocket is commonly referred to as "scrubbing" and causes substantial abrasion of the portion of the bushing which contacts the sprocket.
Prior art efforts to provide long life bushings have been directed at compensating for such abrasion of the bushings. For example, it has been recommended practice to reverse or turn each bushing after a measured amount of wear, so that such wear occurs on different portions of the bushing surface.
Heretofore, such reversing or turning of the bushing required time consuming disassembly and reassembly of the track chain, which is, of course, undesirable. It is desirable to be able to rotate the bushings to present another wear surface thereof to the sprocket with the track chains completely assembled and in place on the vehicle.
Examples of methods and apparatus for turning bushings are disclosed in U.S. Pat. No. 3,915,036 granted Oct. 28, 1975; U.S. Pat. No. 4,002,090 granted Jan. 11, 1977 which is a division of U.S. Pat. No. 3,915,036; and U.S. Pat. No. 4,050,141 granted Sept. 27, 1977 which is a continuation of abandoned U.S. Application Ser. No. 617,346 filed Sept. 29, 1975 which was a division of U.S. Pat. No. 3,915,036, all of which had Harold W. Vanlandingham, Roger L. Boggs, David A. Bullock, and James N. Maytum as common joint inventors.
In U.S. Pat. No. 3,915,036 a clamp member is connected to the bushing and a hydraulic cylinder is connected to the clamp member to apply the force required to turn the bushing. The clamp member has two parts adapted to encircle a bushing of a preselected size. The two parts are placed on the bushing and bolted together and a third part is moved by screws into engagement with the worn portion of the bushing, which is time consuming and inefficient. While the apparatus effectively turns the bushing either a very high pressure pump or a large cylinder must be used.
On a track suitable for use with a D9 track-type tractor manufactured by Caterpillar Tractor Co., the links are pressed onto the bushings with an interference about 0.2 mm (0.008 inch). When the apparatus of U.S. Pat. No. 3,915,036 is employed to turn these bushings, the cylinder has about a 200 mm (8.0 inch) diameter and uses a pump which delivers about 69,000 kPa (10,000 psi) as compared to the 35,000 kPa (5,000 psi) or less normally used in the vehicle hydraulic systems. Such high pressure can mobilize nuts, bolts or other machine parts, tools or equipment and cause injury if a leak developed. Using a lower output pump would require an even larger cylinder which would require partial or total disassembly of the track. It is desirable to have a compact bushing turning tool which does not require higher than normal fluid pressures.
A solution to the high fluid pressure problem is disclosed in U.S. Pat. No. 4,002,090 where an elongated arm member is connected to the clamp member. The extended end of the arm is positioned to be contacted by a body which is fixed relative to the vehicle, upon forward motion of the vehicle. Thus, the forward driving force of the vehicle is utilized to the bushing. While high fluid pressure is not required, the bushings are turned while the vehicle is in motion which is itself undesirable since it means mobilizing a mass of about 35,000 kg (76,000 lb.). It is desirable to rotate the bushings of a completely assembled track without mobilizing the entire vehicle.
A method for turning bushings is described in U.S. Pat. No. 4,050,141 using the apparatus of U.S. Pat. Nos. 3,915,036 and 4,002,090 and similar apparatus. This method has the advantages of the apparatus used to perform the method and, unfortunately, the disadvantages also. Thus, the method employs a high pressure pump, a large cylinder or a moving track chain or it requires at least partial disassembly of the track. It is therefore desirable to have a bushing turning method which is simple to perform on a stationary, fully assembled track without the use of high fluid pressure or large cylinders.